(a) Field of the Invention
The present invention relates to a zoom lens system and, more particularly, to a zoom lens system for a compact camera having a high zoom ratio and having three lens groups.
(b) Description of the Related Art
Automatic compact cameras have recently been provided with zoom lens system.
Generally, zoom lens systems for compact cameras can be divided into two types: a first type with two lens groups and a second type with three lens groups. The first type with two lens groups is compact and lightweight, but does not provide a high magnification. Accordingly, the first type with two lens groups is used for zoom lens systems with a zoom ratio of less than 3.0.
The second type with three lens groups is subdivided into two classes. The first class includes, when viewed from the object side, a first lens group with a negative refractive power, a second lens group with a positive refractive power and a third lens group with a negative refractive power. The second class includes a first lens group with a positive refractive power, a second lens group with a positive refractive power and a third lens group with a negative refractive power.
Zoom lens systems of the first class are disclosed in Japanese Publication Nos. Hei 2-201410 and Hei 2-37317. These zoom lens systems can have large aperture and zoom ratios. However, theses zoom lens systems have a considerable total length and a large outside diameter, making them unsuitable for compact cameras.
Zoom lens systems of the second class are disclosed in Japanese Publication Nos. Hei 6-59192, Hei 2-73211, Hei 2-287507 and Hei 4-165319. These zoom lens systems can be conveniently constructed in compact form. However, these zoom lens systems have a zoom ratio of less than 3.0, which makes it difficult to obtain a high zoom ratio.